The present invention relates to a semiconductor integrated circuit and, more particularly, to a voltage detector device incorporated in, e.g., an LSI circuit and used together with a voltage regulator of a power source such as a solar cell whose output voltage greatly varies.
When an LSI circuit is driven using a power source such as a solar cell whose output voltage greatly varies, a voltage regulator is an indispensable component. Since a current consumed in the LSI circuit other than the voltage regulator is as small as about 1.5 V, 1,000 nA, a current consumed in the voltage regulator is preferably 200 nA or less. Variations in output voltage of the regulator are preferably .+-.0.1 V (.+-.7%) or less for 1.5 V. A solar cell voltage regulator is preferably formed in the LSI circuit. Therefore, the occupying area of the voltage regulator on the LSI circuit substrate must be minimized.
A conventional voltage regulator is designed such that at least two series-connected resistors are connected across output terminals of a power source to constitute a voltage divider, an output from the voltage divider is compared with an output voltage from a constant voltage circuit, and a voltage applied to the voltage divider is regulated in response to a comparison output.
In order to form the power source voltage detector device and the voltage regulator having the above-mentioned arrangement in the LSI circuit, current consumption must be limited to 200 nA or less. For this purpose, the resistance of the voltage divider must be as high as several tens of megaohms. However, such a resistance requires a large occupying area in the LSI circuit. It is then impossible to form the voltage regulator on the same substrate or chip of the LSI circuit.